CAM Redundancy for Memory Error Correction

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Solution Overview

Problem

In large memory systems like DRAM and SRAM, the number of defective locations increases over time, exceeding the capacity of content addressable memory (CAM) used for error correction, leading to a need for an efficient method to manage and replace defective entries.

Innovation Solution

An ECC memory system that utilizes a content addressable memory (CAM) and a redundant memory array to identify and replace recurring addresses, using a redundant array element to store corrected data, thereby freeing up CAM entries and extending the memory system's life and reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If CAM is used to store redundant entries for defective memory locations, then error correction capability is improved, but CAM capacity is exceeded when the number of defects increases over time

Engineering Contradiction:

Improveerror correction capabilityVSAvoidCAM capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent implements a mechanism to detect when CAM entries contain recurring defective addresses and systematically removes these redundant entries from CAM. By identifying that certain addresses appear multiple times in CAM (indicating persistent defects), the system discards these duplicate entries and recovers CAM capacity for storing new defective location mappings, thus resolving the capacity exhaustion problem while maintaining error correction reliability

Inventive Principle:

Principle #34Discarding and recovering

Solution Approach 2:

The patent creates duplicate copies of defective address mappings within CAM and then identifies these copies for removal. By copying the same defective address mapping multiple times and then detecting the recurrence, the system can systematically eliminate redundant copies, freeing up CAM entries while preserving the essential error correction functionality for unique defective locations

Inventive Principle:

Principle #26Copying

2Reliability

If the number of CAM entries is increased to handle more defects, then error correction coverage is improved, but device complexity and memory overhead increase

Engineering Contradiction:

Improveerror correction coverageVSAvoidmemory overhead

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent systematically identifies and removes redundant CAM entries containing recurring defective addresses, thereby reducing the total number of CAM entries required. This approach decreases memory overhead and simplifies the error correction structure while maintaining comprehensive coverage by ensuring that only necessary unique mappings are retained in CAM

Inventive Principle:

Principle #34Discarding and recovering

Data Source

PatentUS9389954B2Memory redundancy to replace addresses with multiple errors

Publication Date: 2016.07.12 ASCALE TECHNOLOGIES LLC

AI summary

A method and apparatus are provided for error correction of a memory by using a first memory (18), second memory (14), and redundant memory (19) to perform error correction code (ECC) processing on data retrieved from the first memory (18) by using the redundant memory (19) to replace entries in the second memory (14) having repeat addresses, thereby freeing entries in the second memory (14) for use in detecting and managing errors identified by the ECC processing.